Symantec has told customers of its consumer security products that they should disable a feature in the software before upgrading to Windows XP Service Pack 3 (SP3), or risk crippling their computers.

In a post to a Symantec support forum, Reese Anschultz, a senior manager with the company, said users of Norton Internet Security, Norton AntiVirus and Norton 360 -- the firm's best-selling consumer security software titles -- should switch off the "SymProtect" feature before trying to install XP SP3.

"After a lot of testing, we've reproduced a number of different cases where applying the XP SP3 upgrade adds additional registry keys within already-existing Symantec registry keys," said Anschultz. "We have determined that the SymProtect feature is involved, though this issue is not exclusive to Symantec customers. To help prevent this issue from occurring, you should disable SymProtect prior to installing the Windows XP SP3 upgrade."

Anschultz also provided instructions for disabling SymProtect in various Norton-labeled titles.

SymProtect, which Symantec bills as technology designed to protect its security software from being hacked by malware, is tagged with the added description of "tamper protection" in some of its consumer products.

Anschultz said last Friday that Symantec was still trying to pin down why the XP SP3 upgrade was adding spurious entries -- in some cases thousands of them -- to some users' Windows registries. "We are still trying to understand why the upgrade is adding these keys," he said in the post.

Within hours of Microsoft releasing Windows XP SP3 to its Windows Update service, users started reporting problems that included empty Device Managers and broken network connections that cut them off from the Internet or wireless networks. Users quickly identified the cause as large numbers of bogus keys -- all starting with nonsense characters such as " "$%&" -- that had flooded the registry.

Symantec has repeatedly denied that the problem was its fault, while Microsoft has just as regularly declined to comment. Last week, Symantec blamed a Microsoft file named fixccs.exe for spawning the errant registry entries; fixccs.exe is part of the XP SP3 upgrade package.

Tuesday, however, a Symantec spokeswoman said that it was a combination of fixccs.exe and her firm's SymProtect that caused the problem on some systems. "Fixccs.exe adds registry keys during the SP3 update process and then attempts to delete them," said Cecilia Daclan in an e-mail Tuesday morning. "SymProtect prevents changes to the registry keys. Thus, it prevents the deletion of the keys added by fixccs.exe."

Symantec continued to claim, however, that the blanked Device Manager problem was not specific to its software. "This issue is not exclusive to Symantec customers," said Daclan. "We've seen reports from various users who are not running Symantec products."

Last week, Symantec said it was working on a stand-alone tool that would delete the extraneous registry entries, and added that it hoped to have something "pretty quickly." As of Tuesday, Symantec had not released the tool. On Friday, Anschultz said the company would use the support forum to point customers to the tool when it was finished.